1. Field of the Invention
The present invention relates generally to a conveyor chain having a multiplicity of links pinned together and each including a flat load-carrying portion for carrying thereon an article to be conveyed by the conveyor chain. More particularly, this invention relates to a low friction coefficient plastic conveyor chain particularly suitable for use in an accumulate conveyor by which articles are accumulated at a given position on the conveyor chain while they are slipping on the flat load-carrying portions during continuous traveling of the conveyor chain, or a sorting conveyor by which articles are sent out from or collected into a given position on the flat load-carrying portions while the conveyor chain travels continuously.
2. Description of the Related Art
In a conveyor chain designed for use in the applications described above, links as a whole or at least flat load-carrying portions of the links are required to have a small friction coefficient so that articles can slip on the flat load-carrying portions. To meet with this requirement, the links or the flat load-carrying portions are conventionally formed from a synthetic resin material composed of a polyacetal resin blended with a fluorine resin or a long-chain alkyl ester-based lubricant.
The conventional plastic conveyor chain has been found unsatisfactory as a container having a relatively unstable bottom configuration, such as a petaloidal-shaped PET (polyethylene terephthalate) bottle, has recently distributed in the market. This is because containers having such unstable bottom configuration are liable to fall over during conveyance or as they are caused to slip on the flat load-carrying portions of the conventional plastic conveyor chain.
To deal with this problem, two approaches have been taken. According to a first prior approach, chamfered front and rear corner edges of each flat load-carrying portion and the spacing between adjacent links are made small so as not to catch the bottoms of the containers. A second approach relies on a satin finishing effected on the load-carrying surface to reduce a contact area relative to the containers, thereby decreasing a frictional resistance between the satin-finished load-carrying surface and the containers.
The first approach is found somewhat successful, but the second approach is not because the satin-finished load-carrying surface becomes worn away in a relatively short time. Since the worn-out load-carrying surface has an increased friction coefficient, causing the container falling-over problem to recur.
From the still unsatisfactory results of the prior approaches, the present inventors have concluded that the links as a whole or at least the flat load-carrying portions of the links need to be formed from a material having a smaller friction coefficient than the materials used in the conventional conveyor chain.